Polysaccharide and process for the production thereof

ABSTRACT

Polysaccharides forming gels are produced by cultivating a microorganism such as Arthrobacter carbazolum FERM 2574 in a suitable medium.

FIELD OF THE INVENTION

The present invention relates to a novel polysaccharide and a processfor the production thereof.

BACKGROUND OF THE INVENTION

Heretofore, various processs for producing a polysaccharide utilizingmicroorganism have been proposed. However, the greater part of theseprocesses was concerned with a viscid polysaccharide and there have beenvery few reports concerning a process for the production of apolysaccharide forming a gel. In addition, the known polysaccharidescharacterized by gel-formation have been produced by utilizing sugars asthe carbon source of a nutrient medium.

SUMMARY OF THE INVENTION

The present invention is based on the following observations:

(1) that microorganisms isolated from various types of soil have anability for producing a polysaccharide forming a gel;

(2) that said microorganisms belong to the genus Arthrobacter;

(3) that the polysaccharide is accumulated in a culture broth when themicroorganisms are cultivated with the nutrient medium;

(4) that the recovered polysaccharide has the property of forming a gel.

According to the present invention, a polysaccharide characterized bygel formation can be produced by cultivating a polysaccharide having gelforming property-producing microorganism belonging to the genusArthrobacter in a medium containing assimilable carbon sources andnitrogen sources until said polysaccharide is substantially accumulatedin the culture, and recovering the accumulated polysaccharide therefrom.

EMBODIMENTS OF THE INVENTION

The microorganisms which can be employed in this invention belong to thegenus Arthrobacter, for example, Arthrobacter carbazolum, which wasisolated from soil and named as above by us. This strain was depositedin the Fermentation Research Institute, Agency of Industrial Science andTechnology, Japan, and assigned the identification FERM-2574, and alsodeposited with the American Type Culture Collection, Rockville, Md.,U.S.A., and assigned the identification ATCC-31258.

The microbial characteristics of said Arthrobacter carbazolum are asfollows:

1. Microscopic Examination

Size: 0.6-0.8 × 1.2-2.7μ

Figure: rod, polymorphic

Gram strain: negative

Spore: negative

Flagella: one to three peritrichous flagella

2. Cultivation Examination with Medium

Bouillon agar plate culture: almost circular, rugose, undulate,semi-transparent, sticky;

Bouillon agar slant culture: good growth, rugose, spreading, sticky;

Bouillon broth culture: ring, pellicle, forming slight sticky sediment;

Bouillon agar stab culture: filiform, good growth in upper part;

Bouillon gelatine stab culture: growth only on surface, no liquefaction(cultivated for 40 days at 22° C.);

Growth in litmus milk: slightly alkaline, no coagulation;

Growth in potato-dextrose agar medium: moderate growth, no pigment;

3. Physiological Properties

Optimum pH for growth: 8-9

Optimum temperature for growth: 37° C.

pH range for growth: 5.5-9.5

Temperature range for growth: 24°-43° C.

Formation of indole: no

Formation of H₂ S: yes

Formation of gas and organic acid from carbohydrate: no

Degradative ability of cellulose: no

Hydrolitic ability of starch: yes

Reduction of nitrate: yes

Availability of citric acid: yes

Methyl red test: negative

Voges-Proskauer test: negative

Formation of catalase: yes

Formation of ammonia: yes

Liquefaction of gelatin: no (cultivated for 50 days)

Availability of ammonium salt and nitrate: yes

Oxidase test: positive

Halophobicity against salt: no

Formation of urease: no

Growth in both aerobic and anaerobic conditions

Availability of agar: no

4. Availability of Various Carbon Sources

Glucose, fructose, maltose, glycerol,

glycogen, methanol, ethanol and propanol

were utilized for growth.

Acid and gas formation tests were done according to the method of Hughand Leifson (R. Hugh and E. Leifson: J. Bact., 66, 24 (1953)). As aresult, acid and gas formation were not found in both aerobic andanaerobic conditions. Furthermore, in the case of using a fermentationtube with Ayer's and Barsiekov's medium (J. M. Pelczar: Manual ofMicrobiological Methods (McGraw-Hill) (1957)), acid and gas formationwere not found.

None of the arabinose, xylose, galactose, mannose, sucrose, lactose,trehalose, raffinose, salicin, mannitol, inositol or sorbitol wasutilized.

On the basis of microbiological characteristics above described, thisstrain was compared with those described in the 7th edition of Bergey'sManual of Determinative Bacteriology, and was considered to belong tothe genus Arthrobacter from such points as polymorphic figure and soilbacteria which is in coccus-form in the later stage of the cultivation.As strains belonging to Arthrobacter which can utilize nitrates andammonium salts as nitrogen sources and also possess hydrolitic abilityof starch, Arthrobacter globiformis and Arthrobacter pascens are listed.The strain isolated by us is considered to resemble Arthrobacter pascensfor the reason that it becomes remarkably sticky with the advance ofgrowth. However, this strain is remarkably different from Arthrobacterpascens in view of action against gelatin and growth temperature, etc.The following differences between the two strains are listed in thefollowing table.

    ______________________________________                                                      Arthrobacter                                                                              Strain                                                            pascens     isolated                                            ______________________________________                                        Growth at 37° C                                                                        no            yes                                             Liquefaction of gelatin                                                                       yes           no                                              Growth on the surface of                                                      a liquid medium no            yes                                             Assimillation of carbazole                                                                    no            yes                                             ______________________________________                                    

From these results, this strain was identified as a new speciesbelonging to Arthrobacter, and named Arthrobacter carbazolum todistinguish it from already-known strains. This new strain has beendeposited as indicated above.

In the present invention, all strains belonging to the genusArthrobacter which possess an ability to produce a polysaccharide havinggel forming property can also be used as well as artificial or naturalmutants of the strain described above.

In the case of cultivating this strain, such generally utilizedsubstances as saccharides (for example, glucose, starch, etc.) can beused as carbon sources. In addition, acetic acid and such derivativesfrom petrochemistry as ethanol, glycerol, propanediol, butanediol,ethyleneglycol, etc., can also be used as carbon sources. As a nitrogensource, potassium nitrate, ammonium nitrate, ammonium sulfate, ammoniumchloride, ammonium phosphate, polypeptone, carbazole, etc., can be used.As inorganic salts, dipotassium hydrogen phosphate or disodium hydrogenphosphate and potassium dihydrogen phosphate, etc., can be used, and asa source of a trace elemental metal, magnesium sulfate, ferrous sulfate,etc., can be used. A medium prepared by adding the above-describedcomponents into tap water was inoculated with the new strain, andcultivated in an aerobic condition by reciprocal shaking.

After completion of the cultivation, the polysaccharide accumulated in aculture broth can be harvested by various methods according to thepurpose of use. For example, a water-soluble solvent such as methanol,ethanol, isopropanol, acetone, tetrahydrofurane, etc., is added in ahigh viscous broth to precipitate the polysaccharide with the cells, andafter drying this precipitate can be used as a crude product.

When a solid material in the broth such as microbial cells isdisadvantageous to the purpose of use, an appropriate amount of water isadded before refining the broth, and the broth is heated. Subsequently,the polysaccharide is recovered from the solution obtained bycentrifugation of the broth.

In refining, such routine methods for separation of the polysaccharidefrom impurities as condensation, precipitation with the above-describedwater-soluble solvent, precipitation with ammonium sulfate, washing,centrifugation, column chromatography, extraction with solvent,dialysis, etc., can be used singly or in combination. For example, aftercultivation, an appropriate amount, preferably 3-10 times the amountbased on the amount of the broth, of water is added into the broth, andthe resultant mixture is heated to 45° to 65° C. The supernatant fluidis obtained by centrifugation of the broth. Subsequently, an aliphaticquarternary ammonium salt such as cetyl trimethyl ammonium bromide,etc., is added into this supernatant to precipitate the polysaccharide.The polysaccharide separated is washed with 85 to 95% methanol orethanol saturated with sodium chloride or potassium chloride, etc.Thereafter, the polysaccharide is swelled by addition of water. Afterwashing with acetone, etc., the polysaccharide is subjected to drying.

On the other hand, the polysaccharide can also be obtained by theaddition of from 5 to 10 times the amount of water-soluble solvent suchas acetone to precipitate the polysaccharide, or by spray-drying afterdesalting of the above supernatant by ultra-filtration or with an ionexchange resin such as Amberlite IR-120 B, Amberlite IRA-410, etc., andconcentration. When a polysaccharide with higher purity is required,such procedures as deprotein using a mixture of chloroform and isoamylalcohol (4:1) or dialysis can be applied in addition to theabove-described procedures.

The polysaccharide thus obtained was studied on a physiochemical basis,and the results are summarized as shown below.

This polysaccharide does not correspond to the already-known compoundsand therefore, was found to be a new compound.

(1) Elemental analysis

H: 5.50%; C: 38.02%; N: 0%.

(2) molecular weight

Molecular weight was measured by column chromatography using cephalose2B (Pharmasia Co., Ltd., Sweden). The polysaccharide obtained was elutedin void-volume, so molecular weight was estimated as at least above2,000,000. Furthermore, limiting viscosity was measured in the presenceof sodium chloride (1 × 10⁻³ Mole), and as a result, [η] was 29.0 dl/gat 25° C. FIG. 2). This value was applied to Staudinger's expression.From this result, the mean molecular weight was found to be about8,000,000.

(3) Specific rotatory power

    [α].sub.D.sup.23 = +20° - +35° (0.1% aqueous solution, l = 0.1)

(4) Infrared absorption spectrum

IR absorption spectrum obtained with the method of KBr pellet is shownin FIG. 1.

(5) solubility in solvent

The polysaccharide is not dissolved in organic solvents such asmethanol, ethanol, acetone, ether, etc., and forms a gel in water. It isdifficult to dissolve in water even at a low concentration (below 0.1%)and turns to a sticky solution when heated. A heated solution iscolorless and transparent.

(6) Classification by acidity

The pH value of an aqueous solution of the polysaccharide solubilized asabove-described was 3.0 to 3.5. Moreover, a precipitate was formed byadding cetyl trimethyl ammonium bromide. These results show that thispolysaccharide is acidic.

(7) Color reaction

Blueish green by anthrone reaction.

(8) Color of polysaccharide

Colorless and transparent in dry condition and white in powder form.

(9) Melting point

No melting point; carbonization occurred when it was heated to about235° C. It carbonized completely at about 280° C.

(10) viscosity

From the result of measurement of specific viscosity with a Ubbelohdetype viscometer, ηsp was found to be 13 (C = 0.1, 30° C.).

The relation between a reduced viscosity and a concentration of thepolysaccharide, especially the effect of sodium chloride on a reducedviscosity was studied, and the result is shown in FIG. 2. Themeasurement of viscosity was carried out by using a Ubbelohde typeviscometer at 25° ± 0.01° C.

In addition, the effect of pH on viscosity was studied. From theresults, it was found that viscosity was increased remarkably at aboutpH 3 and increased to 50 times compared with the value at pH 7 (FIG. 3).The measurement of viscosity was carried out with a B-type rotatoryviscometer (Tokyo Keiki Co., Ltd.) at 30 r.p.m., a temperature of 25° ±0.01° C. and 0.1% (w/v) of sample concentration. Agar, one of thesamples, was dissolved by treating at 100° C. for 20 minutes. The othersamples were treated at 60° C. for 10 minutes in order to solubilize.Adjustment of pH was done by adding dilute hydrochloric acid or dilutesodium hydroxide. The remarkable increase of viscosity was also observedby adding sodium chloride too (FIG. 4). Experimental conditions were thesame as in the case of studying the effect of pH. These characteristicsare specific to the polysaccharide of this invention.

(11) Physical characteristics of polysaccharide gel

The polysaccharide forms a gel containing water at the concentration ofmore than 0.5% of polysaccharide and possesses the characteristic ofsolubility with heating and being coagulable with cooling, andfurthermore, it forms a gel only by contacting with water at roomtemperature (as at about 21° C.).

Table 1 shows the results of physical properties of polysaccharide gels.Measurements were carried out as described below.

Water was added to a sample powder, and the resulting mixture was heatedat 60° C. for 30 minutes with stirring. After cooling at roomtemperature (about 21° C.) for 1 hour, breaking strength (gel strength)and solidity of the gel were measured by using a curd meter (M-301AR-type, Iio Denki Co., Ltd.).

                  Table 1.                                                        ______________________________________                                        Effect of polysaccharide                                                      concentration on gel strength                                                                     Breaking                                                          Concentration                                                                             strength    Solidity                                      Sample  (%)         (dyne/cm.sup.2)                                                                           (dyne/cm.sup.2)                               ______________________________________                                                0.5         2.25 × 10.sup.4                                                                     9.90 × 10.sup.3                         agar    1.0         1.08 × 10.sup.5                                                                     8.03 × 10.sup.4                                 2.0         5.56 × 10.sup.5                                                                     3.19 × 10.sup.5                                 0.5         <3.0 × 10.sup.3                                                                     <1.0 × 10.sup.3                         poly-   1.0         4.43 × 10.sup.4                                                                     8.65 ×]10.sup.3                         saccharide                                                                            2.0         5.78 × 10.sup.5                                                                     3.28 × 10.sup.4                         ______________________________________                                    

The polysaccharide used as a sample was produced by using a fermentationmedium containing ethanol and carbazole as main components, and washedwith ethanol and acetone.

As shown in Table 1, the polysaccharide gels were soft and viscous incomparison with agar gels, and are assumed to have substantialelasticity from the fact that the gels are difficult to break. Actually,from the result of measurements of texture by using a rheolometer(produced by Iio Denki Co., Ltd.), it was found that the elasticity ofthe polysaccharide gels was as strong as that of polyurethane.

When a frozen gel was thawed, no phenomenon of leaving water wasobserved, and the gel was restored to the original state.

The polysaccharide obtained by the present invention has an ability toform a gel with water, moreover, it has a specific property to form agel even with a solution containing a water-soluble organic solvent athigh concentration. Table 2 shows the result of measurements of theeffect of water content on gel formation. The measurements were carriedout according to the following procedure. Polysaccharide powder (15milligrams) was placed in a test-tube, and various amounts of organicsolvent (1 milliliter) were added. After heating at 60° C. for 30minutes, a solution was cooled and then yes (+) or no (-) on gelformation was checked. Sign ± designates jelly form.

                  Table 2.                                                        ______________________________________                                        Minimum amount of water required for                                          geling of oraganic solvent                                                    Solvent                                                                       Water   Methanol Ethanol  Isopropanol                                                                            Acetone                                    ______________________________________                                        50%(v/v)                                                                              +        +        +        +                                          40      +        +        +        +                                          25      +        +        +        +                                          20      +        +        ±     -                                          15      +        +        -        -                                          10      ±     -        -        -                                           0      -        -        -        -                                          ______________________________________                                    

As shown in Table 2, gel formation did not occur in the absence ofwater, but a gel was formed in the presence of a relatively small amountof water. Next, the effect of ethanol concentration on breaking strength(gel strength) was studied. The results are shown in FIG. 5, indicatingthe maximum strength at 50-75% of ethanol concentration. In a referencetest using agar or gelatin, gel formation occurred up to a concentrationof 50%, but these samples were precipitated at a concentration of morethan 50%. On the other hand, the polysaccharide obtained by thisinvention formed a gel with 85% of ethanol. Conditions for forming a gelare described in the following. Polysaccharide powder was mixed with thesolution containing various amounts of ethanol, and polysaccharide gelswere prepared by heat treatment at 60° C. for 30 minutes. Agar gels wereprepared as follows. Powder was solubilized by heat treatment at 100° C.for 10 minutes, and ethanol was added to the solution after cooling at60° C. Gelatin gels were prepared in the same manner as agar, except theheat treatment was done at 60° C. for 20 minutes. Increase of breakingstrength was observed by adding sodium chloride (0.1% to 10%concentration).

Further, stress relaxation of a polysaccharide gel was compared withthat of agar gel. The measurement was carried out by using a rheolometer(RMT-1300, Iio Denki Co., Ltd.) at a sample concentration of 2.0% (w/v)adjusting with water as a solvent.

                  Table 3.                                                        ______________________________________                                        Stress relaxation                                                             Property  Polysaccharide gel                                                                           Agar gel                                             ______________________________________                                                γ1                                                                            1.01 ×10.sup.5 dyne/cm.sup.2                                                           2.27 ×10.sup.5 dyne/cm.sup.2               Modulus of                                                                            γ2                                                                            3.26 × 10.sup.4                                                                        1.53 × 10.sup.5                            elasticity                                                                            γ3                                                                            1.83 × 10.sup.4                                                                        9.88 × 10.sup.4                                    η1                                                                              ∞dyne·sec./cm.sup.2                                                           ∞dyne·sec./cm.sup.2               Coefficient                                                                           η2                                                                              5.38 × 10.sup.6                                                                        6.74 × 10.sup.7                            of viscosity                                                                          η3                                                                              3.75 × 10.sup.5                                                                        1.13 × 10.sup.7                                    τ1                                                                              ∞sec.    ∞sec.                                      Relaxation                                                                            τ2                                                                              165.0          440.0                                            time    τ3                                                                               20.5          115.0                                            ______________________________________                                    

(12) Components of polysaccharide

Purified polysaccharide was hydrolized by 1N-sulfuric acid at 100° C.for 6 hours, and the reaction mixture was neutralized by adding bariumcarbonate. After centrifugation, the resulting supernatant was analyzedby paper chromatography, thin-layer chromatography and gaschromatography of a trimethylsilyl derivative. Table 4 shows the R_(f)value of the decomposed polysaccharide in paper chromatography, and FIG.6 shows a gas chromatogram of the trimethylsilyl derivative. From theseresults, it was found that the polysaccharide of this inventioncomprises glucose, mannose, unknown neutral sugar and unknown acidicsugar.

                                      Table 4                                     __________________________________________________________________________    R.sub.f value of components polysaccharide in                                 paper chromatography                                                          Constituent sugar                                                                       Solvent for development                                                                    R.sub.f value                                                                       Reagent for detecting                            __________________________________________________________________________    glucose                0.13  p-anisidine, silver nitrate                      mannose                0.19  p-anisidine, silver nitrate                                butanol:acetic acid:water                                           unknown neutral                                                               sugar     = 4 : 1 : 1  0.46  silver nitrate                                   unknown acidic               p-anisidine, bromocresol                         sugar                  0.55  green                                            glucose                0.60  p-anisidine, silver nitrate                      mannose   isopropanol:pyridine                                                                       0.65  p-anisidine, silver nitrate                                :water:acetic acid                                                  unknown neutral                                                                         =8 : 8 : 4 :1                                                                              0.81  silver nitrate                                   sugar                                                                         unknown acidic         0.75  p-anisidine, bromocrezol                         sugar                        green                                            __________________________________________________________________________

Structural elucidation of unknown neutral sugar (designated as HA-1hereafter) and unknown acidic sugar (designated as HA-2 hereafter) wascarried out as described below.

(1) Identification of HA-1

Hydrolyzed product of the polysaccharide was applied to a charcoalcolumn chromatography, and eluted with water, 10% of ethanol and ethanolin this order. Glucose and mannose were found in the water-elutedfraction, and HA-1 and HA-2 were found in 10% ethanol-eluted andethanol-eluted fractions, respectively.

The 10% ethanol-eluted fraction was concentrated to dryness and waspurified by ion exchange column chromatography (Dowex 1x8, borate type),and HA-1 was isolated from the resulting 0.015 mole of potassium borateeluted fraction. HA-1 was unstable and difficult to crystallize, so anoxidation reaction with bromine was made. That is, 40 milligrams of HA-1was dissolved in 2 milliliters of bromine water in the presence of 240milligrams of strontium carbonate, and reacted at 30° C. overnight.After the reaction, the reaction mixture was filtered and bromine in thefiltrate was removed under a reduced pressure. Subsequently, thefiltrate was treated with silver carbonate. After removal of theresulting precipitate, the reaction product was applied to ion exchangecolumn chromatography (Dowex 1x8, acetate-type) to obtain crude crystalsfrom 2 moles of an acetic acid eluted fraction. The crude crystalsobtained were recrystallized in acetone-ethyl acetate to form 20milligrams of colorless needle crystals. The crystals were analyzed byseveral physical methods, and results are shown below. FIG. 7 shows theIR absorption spectrum of the crystals.

(a) Melting point: 130°-142° C.

    ______________________________________                                        (b) Elemental Analysis:                                                              Calculated (C.sub.6 H.sub.10 O.sub.5)                                                          Found                                                 ______________________________________                                        C        44.44%             44.59%                                            H        6.22%              6.14%                                             O        49.34%             49.31%.                                           ______________________________________                                    

(c) Absorption range in IR absorption spectrum (KBr tablet method)

3200-3450 cm⁻¹ (OH), 2850-3000, 1460, 1360, 1342 cm⁻¹ (CH, CH₂, CH₃),1770, 1755 cm⁻¹ (C = O in lactone), 1405 cm⁻¹ (OH), 1290, 1250, 1220,1160, 1135, 1078, 1043, 1015 cm⁻¹ (C--OH, COO, CO in C--O--C), 955 cm⁻¹,906 cm⁻¹, 843 cm⁻¹, 768 cm⁻¹.

Absorption range in NMR spectrum ##STR1##

8.67 τ (d, J = 6 Hz, CH₃ of C₅ position), 6.39 τ (d, J = 5.5 Hz, CH₂ OHof C₃ position), 5.97 τ (s, OH of C₃ position), 5.65 τ (t, J = 5.5 Hz,CH₂ OH of C₃ position), 5.41 τ (d, J = 8 Hz, CH of C₂ position), 5.38 τ(q, J = 6 Hz, CH of C₄ position), 5.00 τ (d, J = 8 Hz, OH of C₂position).

An absorption range of HA-1 which is a compound before oxidation withbromine, in NMR spectrum (solvent: D₂ O) was as follows: 8.76 τ (d, J =6.5 Hz, CH₃ of C₅ position), 6.40 τ (s, CH₂ OH of C₃ position), 5.93 τ(d, J = 5 Hz, CH of C₂ position), 5.61 τ (q, J = 6.5 Hz, CH of C₄position), 4.70 τ (d, J = 5 Hz, CH of C₁ position).

Based on the above-described analysis, the product derived fromoxidation of HA-1 was identified as dihydrostreptosonic acidmonolactone, and HA-1 was identified as dihydrostreptose. Chemicalstructure of dihydrostreptose is shown below. ##STR2## (2) Structuralanalysis of HA-2

(A) Estimation of structure

After concentration of the ethanol eluted fraction in charcoal columnchromatography, the concentrates were treated by ion exchange columnchromatography (Dowex 1x8, acetate type). From the 5 moles of theresulting acetic acid eluted fraction, a mixture of acidic-type andlactone-type HA-2 was obtained. First, in order to isolate thelactone-type, silica gel column chromatography was carried out, andcrude crystals of lactone-type were obtained from the eluted fraction(benzene:ethyl acetate = 2:1). The crude crystals were recrystallized inethyl acetate-hexane to form 100 milligrams of colorless needlecrystals.

Results of analysis of the crystals of lactone-type of HA-2 were asfollows. FIG. 8 and FIG. 9 show the IR absorption spectrum and NMRspectrum of the crystals, respectively.

(1) Melting point: 136°-137° C.

    ______________________________________                                        (2) Elemental Analysis:                                                              Calculated (C.sub.9 H.sub.14 O.sub.6)                                                          Found                                                 ______________________________________                                        C        49.54%             49.68%                                            H        6.47%              6.34%                                             O        44.00%             43.87%.                                           ______________________________________                                    

(3) absorption range in IR absorption spectrum (KBr tablet method):

3350 cm⁻¹ (OH), 2850-3000, 1440, 1360-1370, 1320-1340 cm⁻¹ (CH, CH₃),1730-1760 cm⁻¹ (C = O in lactone), 1258, 1215, 1085, 1065, 1040 cm⁻¹(C--OH, COO, C--O in C--O--C), 975 cm⁻¹ (terminal CH₃), 918, 780 cm⁻¹(pyranose ring), 885 cm⁻¹ (CH except for anomer CH), 840 cm⁻¹ (anomerCH), 810 cm⁻¹. ##STR3##

Based on the results above-described, the crystals of lactone-type HA-2were elucidated as a compound in which 6-deoxy hexose and lactic acidform an ether linkage, and a carboxyl group of lactic acid forms alactone linkage with a hydroxyl group of 6-deoxy hexose. In order toelucidate the more detailed structure, various kinds of derivatives ofHA-2 were prepared, and then these derivatives were analyzed by NMRspectrometry. The methods of preparation of derivatives are describedbelow, and the results of NMR spectrometry are shown in Table 5. D₆-acetone was used as solvent in measuring the NMR spectra.

(a) Synthesis of acetyl derivative of HA-2 (lactone-type) (III)

Crystals of lactone-type HA-2 (34 milligrams) were dissolved in 1milliliter of a mixture solution (acetic anhydride:pyridine = 2:1), andreacted overnight at room temperature. After removal of solvent, silicagel column chromatography was carried out. From the resulting elutedfraction (benzene:ethyl acetate = 9:1), 34 milligrams of the derivative(III) were isolated.

(b) Synthesis of methyl glycoside derivative of HA-2 (lactone-type) (IV)

A mixture of acidic-type and lactone-type HA-2 (47 milligrams) wasdissolved in 10 milliliters of a hydrochloride-methanol solution (2.5percent solution), and reaction was carried out for 6 hours underboiling reflux. After the removal of solvent, silica gel columnchromatography was carried out. From the resulting eluted fraction(benzene:ethyl acetate = 5:1), 32 milligrams of the derivative (IV) wereisolated.

(c) Synthesis of methyl ester derivative of HA-2 (acidic-type) (V)

A mixture of acidic-type and lactone-type HA-2 (110 milligrams) wasdissolved in methanol, and mixed with an ether solution of diazomethane.After reaction at room temperature for a night, solvent was removed, andthen subjected to silica gel column chromatography. From the resultingeluted fraction (benzene:ethyl acetate = 7:3), 66 milligrams of thederivative (V) were isolated.

(d) Synthesis of perfect acetyl derivative of methyl ester of HA-2(acidic-type) (VI)

Twenty-four milligrams of the compound (V) obtained by theabove-described reaction (c) were dissolved in 1 milliliter of a mixturesolution (acetic anhydride:pyridine = 2:1), and reaction was carried outovernight at room temperature. After the removal of solvent, silica gelcolumn chromatography was carried out, and 20 milligrams of compound(VI) were isolated from the eluted fraction (benzene:ethyl acetate =9:1).

(e) Synthesis of partial acetyl derivative of methyl ester of HA-2(acidic-type) (VII)

Twenty-three milligrams of the compound (III) obtained by the reaction(a) were mixed with a small amount of water to open the lactone ring,and an ether solution of diazomethane was added, followed by a reactionat room temperature overnight. After the removal of solvent, silica gelcolumn chromatography was carried out, and 17 milligrams of the compound(VII) were isolated from the resulting eluted fraction (benzene:ethylacetate = 7:1).

From the results of analysis shown in Table 5, structures of HA-2(acidic-type) (I), HA-2 (lactone-type) (II) and various kinds ofderivatives were estimated as follows:

    ______________________________________                                         ##STR4##                                                                     HA-2 (acidic-type) (I)                                                                     R.sub.1R.sub.2R.sub.3R.sub.4H                                    HA-2 (lactone-type) (II)                                                                   R.sub.5R.sub.6H                                                  Derivative (III)                                                                           R.sub.5R.sub.6CH.sub.3 CO                                        "(IV)        R.sub.5CH.sub.3, R.sub.6H                                        "(V)         R.sub.1R.sub.2R.sub.3H, R.sub.4CH.sub.3                          "(VI)        R.sub.1R.sub.2R.sub.3CH.sub.3 CO, R.sub.4CH.sub.3                "(VII)       R.sub.1R.sub.2CH.sub.3 CO, R.sub. 3H, R.sub.4CH.sub.3.           ______________________________________                                    

                                      Table 5.                                    __________________________________________________________________________    NMR spectra of various derivatives of Ha-2 (solvent: D.sub.6 -acetone)        Derivative                                                                    Proton II         III      IV       V         VI       VII                    __________________________________________________________________________                          d                  d        d         d                 CH of C.sub.1                                                                        4.90 τ 4.02 τ,                                                                       J.sub.1-2                                                                          5.36 τ                                                                             4.96 τ,                                                                        J.sub.1-2                                                                          4.04 τ,                                                                       J.sub.1-2                                                                          4.08                                                                               J.sub.1-2         position              1.95Hz             2Hz      2Hz       2Hz                                     d -- d             d -- d   d -- d    d -- d            CH of C.sub.2                                                                        6.02 τ 4.72 τ,                                                                       J.sub.1-2, J.sub.2-3                                                               6.00 τ                                                                             6.07 τ,                                                                        J.sub.1-2, J.sub.2-3                                                               4.68 τ,                                                                       J.sub.1-2,                                                                         4.72 τ,            position              1.95Hz 3Hz         2Hz 2Hz  2Hz 3Hz                                           d -- d   d                  d -- d                      CH of C.sub.3                                                                        5.96-6.20 τ                                                                          5.78 τ,                                                                       J.sub.2-3, J.sub.3-4                                                               6.17 τ,                                                                       J.sub.3-4                                                                          6.2-6.4 τ                                                                           6.12 τ,                                                                       J.sub.2-3,                                                                         6.2-6.4 τ          position              3Hz 9-10Hz                                                                             9Hz                3Hz 9Hz                                  d -- d   d        d -- d    d -- d   d -- d    d -- d            CH of C.sub.4                                                                        5.68 τ,                                                                         J.sub.3-4, J.sub.4-5                                                               5.74 τ,                                                                       J.sub.3-4                                                                          5.70 τ,                                                                       J.sub.3-4, J.sub.4-5                                                               6.54 τ,                                                                        J.sub.3-4, J.sub.4-5                                                               5.08 τ,                                                                       J.sub.3-4,                                                                         6.55 τ,            position     10Hz 10Hz                                                                              9-10Hz   9Hz 9Hz   9Hz 10Hz 9Hz 9Hz                                           q        d -- q             d -- q                      CH of C.sub.5                                                                        5.96 τ 5.96 τ,                                                                       J.sub.5-6                                                                          6.28 τ,                                                                       J.sub.4-5, J.sub.5-6                                                               6.24 τ                                                                              6.12 τ,                                                                       J.sub.4-5,                                                                         6.2-6.4 τ          position              6Hz      9Hz 6Hz            9Hz 8Hz                                  d        d        d         d        d         d                 CH of C.sub.6                                                                        8.74 τ,                                                                         J.sub.5-6                                                                          8.74 τ,                                                                       J.sub.5-6                                                                          8.74 τ,                                                                       J.sub.5-6                                                                          8.84 τ,                                                                        J.sub.5-6                                                                          8.88 τ,                                                                       J.sub.5-6                                                                          8.78                                                                               J.sub.5-6         position     6Hz      6Hz      6Hz       6Hz      8Hz       6Hz                            q        q        q         q        q         q                 CH of lactic                                                                         5.41 τ,                                                                         7Hz  5.42 τ,                                                                       6Hz  5.44 τ,                                                                       7Hz  5.70 τ,                                                                        7Hz  5.84 τ,                                                                       7Hz  5.72                                                                               6Hzu.,            acid moiety                                                                                d        d        d         d        d         d                 CH.sub.3 of lactic                                                                   8.48 τ,                                                                         7Hz  8.54 τ,                                                                       6Hz  8.53 τ,                                                                       7Hz  8.68 τ,                                                                        7Hz  8.82 τ,                                                                       7Hz  8.72                                                                               6Hzu.,            acid moiety                                                                   __________________________________________________________________________

(B) Identification of constituent sugar in HA-2

Confirmation of the constituent sugar in HA-2 was done by the followinganalytical method.

Thirty milligrams of derivative (V) obtained by the above-describedreaction (c) were dissolved in 1 milliliter of water, and 10 milligramsof sodium borohydride were added. After 3 hours of reaction at roomtemperature, an excess of cation exchange resin (Amberlite IR-120 B, Htype) was added to the reaction mixture in order to decompose theunreacted sodium borohydride. Supernatant obtained by filtration wasevaporated at a reduced pressure, and methanol was added. By repeatingthis evaporation, the remaining boric acid was removed.

As a result, 20 milligrams of reduction product (VIII) were obtained. Apart of compound (VIII) (10 milligrams) was dissolved in 20 millilitersof anhydrous methylene chloride, and then the reaction atmosphere wasreplaced by argon gas. After cooling to -78° C., 4 milliliters of borontrichloride were added, and reacted overnight. After the reaction,methanol was added to the reaction mixture to decompose borontrichloride, and solvent was removed. Methanol was added to the residue,and evaporated at a reduced pressure. This evaporation was repeated. Theresidue was dissolved in water and deionized with an ion exchange resinto concentrate and dry. By this procedure, 7 milligrams of sugar alcohol(IX) derived from the constituent sugar of HA-2 were isolated. From theresult of the analysis with gas chromatography of a trimethylsilyl oracetyl derivative of the sugar alcohol (IX), it was found that retentiontime of these derivatives was coincident with that of variousderivatives of L-rhamnitol prepared by the reduction of L-rhamnose. Inaddition, IR absorption spectrum and NMR spectrum of the acetylderivative (X) also coincided with that of the acetyl derivative ofL-rhamnitol. Accordingly, the constituent sugar of HA-2 was identifiedas L-rhamnose. Structures of various derivatives used in thisidentification process are as follows:

    ______________________________________                                         ##STR5##                                                                             Reduction product (VIII) R.sub.1R.sub.2R.sub.4R.sub.5H R.sub.3CH.s            ub.3 CHCH.sub.2 OH Sugar alcohol (IX) R.sub.1R.sub.2R.sub.3R.sub.4            .sub.5H Acetyl derivative of sugar alcohol (X) R.sub.1R.sub.2R.sub            .3R.sub.4R.sub.5CH.sub.3 CO                                           ______________________________________                                    

(c) confirmation of the site of ether linkage between L-rhamnose andlactic acid

Ten milligrams of the reduction product (VIII) were dissolved in 1milliliter of a mixture solution of acetic anhydride and pyridine (2:1),and reaction was carried out overnight at room temperature. After theremoval of solvent, the reaction product was purified by silica gelcolumn chromatography, and 10 milligrams of acetyl derivative (XI) wereisolated.

This compound (XI) was applied to gas mass-spectroscopy, and fragmentsof M-145 and M-159 were observed. From this result, it was confirmedthat lactic acid is joined by an ether linkage at the C₃ position ofL-rhamnose. Assumptions in regard to the fragments are discussed below.##STR6##

Derivative (XI)

Based on the above-described analytical results, the structure of HA-2was concluded to be 3-O-(1'-carboxyethyl)-L-rhamnose, a new acidicsugar. This is shown below: ##STR7##

From these results, it was found that the constituent sugars of thepolysaccharide obtained by the present invention are glucose, mannose,dihydrostreptose and 3-O-(1'-carboxy ethyl)-L-rhamnose, and the molarratio of these constituent sugars in the polysaccharide was found to be10:10:1-3:3-8 depending on the result of gas chromatography of thetrimethylsilyl derivatives.

In addition, this polysaccharide contains an O-acetyl group, and itscontent was found to be 8-14 weight percent calculated as acetic acidfrom the result of gas chromatographic analysis of acetic acid, whichwas formed in the incubation of the polysaccharide with 1N-sodiumhydroxide for 1 hour at 40° C.

The polysaccharide obtained by the present invention not only possessesviscidity, but also forms a gel having a different property from that ofagar. In the gel formation, the treatment of heating or cooling is notalways necessary, that is, a gel can be formed only by contacting thepolysaccharide with water at room temperature. Moreover, thispolysaccharide has the property of forming a gel at a low concentration,and addition of a cross-linking agent and adjustment of pH are notneeded to form a gel. In addition, this polysaccharide can form a gelimmediately at a low temperature even in the presence of an organicsolvent such as alcohols, organic acids and sugars, or water-solublecompounds such as salts. In this case, gel forming ability of thispolysaccharide is not affected even if the water-soluble compound ispresent in a saturated concentration.

In the formed gel, the phenomenon of water release when the frozen gelis thawed is not observed. In addition, the gel has excellentwater-retaining ability.

The polysaccharide of this invention shows a remarkable increase ofviscosity in a diluent solution as described in FIG. 10. This propertyis specific to this polysaccharide. Further, the diluent solution has athixotropic property.

The novel polysaccharide of this invention can be utilized in variousfields by taking into consideration its specific properties, forexample, as a thickener and gelling agent.

One advantage of this invention is that the fermentation material,especially the carbon source, can be selected with regard to the usemode of the polysaccharide.

Typical examples of this invention are shown below.

EXAMPLE 1

Arthrobacter carbazolum (FERM-2574, ATCC-31258) was inoculated withplatinum loop in a 500 milliliter Sakaguchi flask containing ethanol(1.56%), carbazole (1%), K₂ HPO₄ (0.2%), MgSO₄.7H₂ O (0.025%) andFeSO₄.7H₂ O (0.001%) in a tap water (pH: 8.0), and the cultivation wascarried out for 4 days at 30° C. by reciprocal shaking.

After the cultivation, an amount of hot water (60° C.) corresponding tonine times the amount of the cultured broth was added to the culturedbroth, and cells were removed by centrifugation (10,000 r.p.m., 30minutes). One third amount (by volume) of cetyl trimethyl ammoniumbromide (2% solution) was added to the supernatant with stirring toprecipitate a polysaccharide. The polysaccharide precipitated wasfiltered, and washed twice with 90% ethanol saturated with sodiumchloride. Subsequently, one fourth amount (by volume) of water based onthe amount of the cultured broth was added to swell, and then washedwith five times amount of acetone. After drying, crude polysaccharide (4grams per liter) was obtained. After dissolving the crude polysaccharidein water (0.1% concentration), cations were removed by using AmberliteIR-120 B, and then one third amount (by volume) of a mixture ofchloroform and iso-amylalcohol (4:1) was added. After mixing thoroughly,a supernatant was obtained by centrifugation. The supernatant obtainedwas dialyzed for 3 days at low temperature in water. After dialysis,vacuum drying was applied and thus purified polysaccharide (3.6 gramsper liter) was obtained.

EXAMPLE 2

An experiment was carried out in the same manner as in Example 1, exceptthat carbazole, one of the fermentation sources, was replaced by 0.8% ofpeptone. As a result, 1.8 grams per liter of polysaccharide wereobtained.

EXAMPLE 3

The same experiment as described in Example 1 was carried out, exceptthat carbazole was replaced by 0.2% of potassium nitrate, 0.01% of cornsteep liquor was also added, and the cultivation period was 48 hours. Asa result, 1.5 grams per liter of crude polysaccharide were obtained.

EXAMPLE 4

The same experiment as described in Example 1 was carried out, exceptthat ethanol and carbazole were replaced by 4% of starch and 0.8% ofpeptone. As a result, crude and purified polysaccharide were obtainedwith yields of 4.2 grams per liter and 3.6 grams per liter,respectively.

EXAMPLE 5

An experiment was carried out in the same manner as in Example 3, exceptthat 1.0% of disodium hydrogen phosphate hydrated with 12 H₂ O and 0.55%of potassium dihydrogen phosphate were used in place of dipotassiumhydrogen phosphate, and 0.2% of ammonium nitrate was used in place ofpotassium nitrate. As a result, crude and purified polysaccharide wereobtained with yields of 6.0 grams per liter and 5.0 grams per liter,respectively.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 shows IR absorption spectrum of the polysaccharide of thisinvention. FIGS. 2, 3 and 4 are graphs of viscosity of thepolysaccharide. FIG. 5 shows the effect of ethanol concentration on thegel strength of the polysaccharide. FIG. 6 shows a gas chromatogram of atrimethylsilyl derivative of a hydrolysate of the polysaccharide(condition of measurement: column 5% Silicone OV-17 on Chromosorb W, 2meter of glass, temperature of 150° C.). FIG. 7 is the IR absorptionspectrum of crystals of the oxidation product of HA-1. FIG. 8 is the IRabsorption spectrum of crystals of the lactone-type of HA-2. FIG. 9 isthe NMR spectrum of crystals of the lactone-type of HA-2. FIG. 10 showsgraphs of viscosity of the polysaccharide solution, etc. (condition: Btype rotary viscometer, 25° C., 30 r.p.m.).

In FIG. 6, 1 and 2 show HA-1; 3 shows an internal standard (xylitol); 4and 5 are mannose; 6 and 9 are glucose and 7 and 8 show HA-2,respectively.

What is claimed is:
 1. Polysaccharide having a gel forming propertywhich is characterized by the following properties: (1) comprising (a)glucose, (b) mannose, (c) dihydrostreptose and (d)3-O-(1'-carboxyethyl)-L-rhamnose, the molar ratio of said constituentsbeing (a):(b):(c):(d) = 10:10:1-3:3-8; and (2) containing an O-acetylgroup in an amount of from 8 to 14 weight percent calculated as aceticacid.